Weak La Niña conditions persisted in the tropical Pacific during December 2017. Sea surface temperatures (SSTs) in the central and eastern equatorial Pacific Ocean have continued to cool during December 2017.
While the ocean (surface and subsurface) signals are fully consistent with a weak La Niña state, some atmospheric patterns have become less consistent during December 2017: The Southern Oscillation
Index (SOI) weakened rapidly during the course of the month and is now in the neutral range (-0.2 for December 2017 as a whole). Similarly, the negative zonal wind anomalies that were present in November in the western Pacific Ocean, signalling enhanced trade wind circulation, have weakened significantly.
In summary, weak La Niña conditions are currently present in the Pacific Ocean, despite weakened atmospheric signals during the course of last month (December 2017). The international consensus is that
La Niña conditions are likely (72% chance) to persist over the next 3 month period (January – March 2018). The models agree however that La Niña is likely to decay rapidly during the following three month period, and a return to ENSO-neutral conditions is most likely (74% chance) over the April – June 2018 period.